Field of the Disclosure
The present invention relates to thermal processing using lasers and more particularly, to thermal processing by transmission of mid infra-red laser light through a semiconductor substrate.
Background Art Discussion
Lasers have been used to perform a wide range of material processing to alter a material in some way, for example, by ablation, melting and annealing. In particular, the material may be heated by the absorption of laser energy until the material evaporates, liquefies, or otherwise changes its state or structure. Laser thermal processing has been used in semiconductor manufacturing to machine, separate, bond and treat semiconductor materials for various applications such as the manufacture of LEDs, laser diodes, and other semiconductor devices. Such applications often present challenges because of the small sizes of these devices, the precision required, and the nature of the semiconductor materials that are used.
One way to provide sufficient laser energy for thermally processing materials during semiconductor manufacturing applications, for example, is to direct laser light with a direct line of sight at the material to be processed. In some cases, however, a direct line of sight may not be possible or may result in a more complex and expensive manufacturing process. Attempts at transmitting laser light through certain types of semiconductor substrates, such as silicon, to process materials on the back side of the substrates have failed because the laser light in the spectral range transmitted by the semiconductor material was not able to be transmitted with sufficient power to effect thermal processing. Such backside processing using conventional methods has been limited to certain types of highly transmissive materials with a wide transmission range and/or ultrashort pulses.
Accordingly, there is a need for a method for thermal processing by transmission of laser light through less transmissive semiconductor materials, such as silicon.